1. Field of the Disclosure
The present disclosure is related to testing of fluids in a wellbore and, in particular, to methods and apparatus for determining acoustic properties of fluids in the wellbore.
2. Description of the Related Art
Exploration for hydrocarbons commonly includes using a bottomhole assembly including a drill-bit for drilling a borehole in an earth formation. Drilling fluid or “mud” used in the drilling may vary in density or “mud weight” for a number of reasons. Such variations can result from changes in the quantity and density of cuttings (particles of formation); changes in the “mud program” at the surface, changes in temperature, etc. Variations in mud density also occur when gas or liquid enter the borehole from the formation. Such influx of formation fluids may likely be the result of formation overpressures or abnormally high pressures.
Pressure detection is useful in drilling operations. Not only does the drilling rate decrease with a high overbalance of mud pressure versus formation pressure, but also lost circulation and differential pressure sticking of the drill pipe can readily occur. More importantly, an underbalance of mud pressure versus formation pressure can cause a pressure “kick.” A well may kick without forewarning. Balanced drilling techniques often require only a fine margin between effective pressure control and a threatened blowout. Additionally, there are situations where it is desired to maintain underbalance to avoid formation damage. Thus, there is a need to measure the properties of the borehole fluid downhole in order to detect, among other things, kicks and inflow of formation liquids.